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CHAPTER 28: Interpretation of Hemodynamic Waveforms

KEY POINTS

Randomized trials have found that use of a pulmonary artery catheter did not influence the mortality of critically ill patients with shock or acute respiratory distress syndrome.

Although measurement of right atrial (central venous) pressure (Pra) is a central component of early goal-directed therapy for septic shock, use of the Pra to guide hemodynamic management is controversial.

Partial wedging can lead to marked overestimation of the pulmonary artery wedge pressure (Ppw) and should be suspected when the measured Ppw exceeds the pulmonary artery diastolic pressure (Ppad). With pulmonary hypertension, partial wedging may be present despite a positive Ppad-Ppw gradient and should be suspected when the latter markedly narrows in comparison with previous values.

Positive end-expiratory pressure (PEEP) and active expiration cause the measured Ppw and Pra to overestimate transmural pressure, with active expiration resulting in greater errors. Simultaneous recording of bladder pressure and Pra (or Ppw) can be helpful for assessing the impact of active expiration on transmural pressure.

Hemodynamic waveforms may be helpful in the diagnosis of certain cardiac disorders: Large v waves in the Ppw tracing are seen in acute mitral regurgitation, but can also occur with hypervolemia. Cardiac tamponade is characterized by equalization of the Ppw and right atrial pressure (Pra) with blunting of the y descent. Tricuspid regurgitation often produces a broad c-v wave and a prominent y descent. Inspection of the Pra during narrow complex tachycardias may be helpful if flutter waves or regular cannon a waves (supraventricular reentrant tachycardia) are seen.

Neither the Pra nor the Ppw are reliable predictors of fluid responsiveness. However, failure of the Pra to fall with spontaneous inspiration indicates that the patient is unlikely to benefit from a fluid challenge.

For several decades, decisions regarding therapy with fluids and vasoactive drugs in the ICU have relied on intravascular pressures obtained with either a central venous catheter (CVC) or pulmonary artery catheter (PAC). Despite this widespread use, the value of invasive hemodynamic monitoring is controversial.1-4 Randomized studies of the PAC in a variety of clinical settings have found neither a positive nor negative impact on mortality.5-11 To some, these results provide compelling evidence against continued use of the PAC.1,2 Others have argued that they establish the safety of the PAC, and that an impact on mortality is an unreasonable benchmark for any bedside monitoring device.12,13 Use of the CVC for hemodynamic monitoring is also controversial. While guidelines for management of patients with septic shock recommend measurement of the central venous pressure (CVP) as a component of early goal-directed therapy,14 some have argued that use of the CVP to guide fluid therapy should be abandoned.3

The increased availability of less invasive tools for bedside hemodynamic assessment, including point-of-care echocardiography and minimally invasive measurement of cardiac output, has clearly reduced the need for invasive monitoring.15,16 Nonetheless, we believe that invasive hemodynamic monitoring ...